Effect of monodansylcadaverine (MDC) and retinoic acid (RA) on epidermal growth factor receptor (EGFR) dimerization induced by EGF treatment in primary cultured periportal hepatocytes (PPH) and perivenous hepatocytes (PVH). After EGF (10 −8 m) treatment at intervals 1 min, 5 min, 10 min, 20 min, 30 min, 1 h, 2 h, and 6 h, proteins were cross‐linked with bis‐(sulphosuccinimidyl) suberate (BS 3 ). Cell membranes obtained from hepatocytes were then lysed and protein samples were immunoblotted with anti‐EGFR antibodies. Band quantitation was performed with National Institutes of Health Image software. (a) Immunodetections of EGFRs (monomer and dimer) are shown. Results represent one typical experiment. Molecular weight markers are indicated on the left. (b) The histogram represents mean ± standard error of the mean of three independent experiments, expressed relative to the peak of EGFR dimer in PPH from MDC treated at 5 min following EGF treatment taken as 100%.